As flat display devices, there have been developed various types of liquid crystal displays (LCDs). Many of them employ an active matrix technique. Along with an increased number of signal lines due to higher resolution of a recent pixel matrix section, a plurality of source drivers are used in many cases.
Such the configuration involves the following problems: (1) A bonding step for attaching the source driver should be carried out an increased number of times, thereby impairing productivity. (2) A pitch between the signal lines is reduced, which is likely to induce defects such as (i) a reduction in a yield rate in the bonding step of the source driver and (ii) corrosion due to a difference in electric potential between terminals. (3) On a display screen of the display device, there appears a boundary between the source drivers due to, e.g., a difference in characteristics between the source drivers or a difference in contact resistance between the terminals.
In order to solve these problems, Patent Literature 1 below discloses a display device which employs a source driver capable of outputting electric signals by terminals whose number is one-third of the number of terminals of a conventional source driver and accordingly eliminates the need for using a plurality of source drivers.
FIG. 16 is a view illustrating an entire configuration of a display device 51. As shown in FIG. 16, the display device 51 includes a pixel matrix section 55 in which pixels are arranged in a matrix of m lines and n columns, a gate driver 53, and a source driver 52 for outputting, as a time-divided driver output signal, a driving signal to each one of red, green, and blue pixels in the pixel matrix section 55. Further, the display device 51 includes a signal distribution device 54 formed monolithically on a TFT substrate. The display device 51 is configured such that the signal distribution device 54 distributes, to signal lines of the pixel matrix section 55, driver output signals outputted by the source driver 52.
FIG. 17 is a view illustrating an internal configuration of the signal distribution device 54. As shown in FIG. 17, the signal distribution device 54 includes (i) distribution lines 57(1,r), 57(1,g), and 57(1,b) through 57(n,r), 57(n,g), and 57(n,b) associated with their corresponding driver output signals Si_1 through Si_n outputted by the source driver 52 (where n is an integer of 2 or greater) and (ii) control lines 59_r, 59_g, and 59_b supplied with switching signals for selecting, among the distribution lines, distribution lines to which the driver output signals Si_1 through Si_n are to be inputted, the distribution lines and the control lines being arranged in a matrix. Note that “r”, “g”, and “b” denote red, green, and blue, respectively.
The distribution lines 57(1,r), 57(1,g), and 57(1,b) through 57(n,r), 57(n,g), and 57(n,b) have respective output terminals connected with the signal lines of the pixel matrix section 55. Further, the distribution lines are connected with respective TFTs 60(1,r), 60(1,g), and 60(1,b) through 60(n,r), 60(n,g), and 60(n,b), each of which serves as a switching element. The control lines 59_r, 59_g, and 59_b are correspondingly connected with gates of the TFTs 60(1,r) through 60(n,r), 60(1,g) through 60(n,g), and 60(1,b) through 60(n,b).
FIG. 18 is a timing chart of signals for carrying out, in the display device 51, time-division driving of three distribution lines, for example, the distribution lines 57(1,r), 57(1,g), and 57(1,b). As shown in FIG. 18, a driver output signal Si_k, which is outputted from the source driver 52 to a pixel in a kth column out of the n columns (where k is an integer of 1≦k≦n), is turned to time-division by switching signals of the control lines 59_r, 59_g, and 59_b. Further, signals thus time-divided are inputted to signal lines for red, green, and blue pixels in a jth line out of the m lines (where j is an integer of 1≦j≦m) which jth line is selected by a scanning signal Vg(j) in the pixel matrix section 55. Note that scanning signals Vg(1) through Vg(m) are signals that the gate driver 12 applies to scanning lines of the pixel matrix section 12.
With this configuration, the source driver 52 can output electric signals by terminals whose number is one-third of the number of terminals of a conventional source driver, and eliminates the need for including a plurality of source drivers.
Patent Literature 2 discloses a shape of a distribution circuit shown in FIG. 19. The distribution circuit disclosed in FIG. 19 includes a switching element 60 having a source electrode and a drain electrode each of which has a comb-like shape. This can substantially increase a channel width. Therefore, this is suitable when an even faster switching speed is required.